Up coming emission regulations for diesel engines are driving original equipment manufacturers (OEMs) to incorporate aftertreatment devices, e.g., exhaust emission control devices, into the exhaust systems in order to comply with these regulations. These exhaust emission control devices could include: catalytic converters (e.g., three-way catalyst, oxidation catalysts, selective catalytic reduction (SCR) catalysts, and the like), evaporative emissions devices, scrubbing devices (e.g., hydrocarbon (HC), sulfur, and the like), particulate filters/traps, adsorbers/absorbers, plasma reactors (e.g., non-thermal plasma reactors), and the like.
A major challenge in meeting the future diesel emission requirements is treating the oxides of nitrogen (NOx) due to the inherently lean exhaust air-to-fuel ratio. One method of treating the NOx is the use of SCR catalysts that use ammonia as the reducing agent. Currently, ammonia is produced on-board a vehicle by injecting aqueous urea into the hot exhaust gas, upstream of the SCR catalyst. The urea decomposes to ammonia in the exhaust system and is absorbed by the SCR catalyst. The ammonia then reduces the NOx to nitrogen (N2) in the presence of the catalyst.
A major drawback of the urea SCR system is the requirement to carry a second fluid, urea, on the vehicle in addition to diesel fuel. In addition, a nationwide urea distribution network must be established and maintained to provide a reliable supply to vehicle operators. Thus, a method to generate ammonia on-board the vehicle, using the available diesel fuel is highly desirable to vehicle manufacturers and operators.